Preact is a lightweight JavaScript library designed as a fast, 3kB alternative to React, offering a similar ES6 API while emphasizing performance, size, and efficiency. Developed by Jason Miller and contributors, Preact aims for compatibility with React through a package called preact-compat, which allows developers to switch between the two without major changes to their codebase. Unlike React, Preact excludes certain features like PropTypes and Synthetic Events to maintain its minimal size, making it ideal for projects where performance and small file size are prioritized. Preact is increasingly adopted by companies like Lyft and Uber and supports all browsers, though it may require polyfills for older versions like IE7 and IE8. While Preact is suitable for small, self-contained apps or Progressive Web Apps, React remains preferable for larger, complex applications due to its extensive ecosystem and features.